In acoustic systems and, in particular, in hearing aids with at least one input (for example a microphone) and at least one output (for example an earpiece) there is the risk of acoustic feedback. With sufficiently high amplification, the system starts to oscillate which is made noticeable by whistling.
Until now, the feedback whistle could, for example, be suppressed by so-called notch filters. With this approach, the loop gain is lowered at the frequency at which feedback whistle might occur. By means of this lowering, the amplitude condition for feedback whistle is no longer fulfilled.
A further possibility for suppressing feedback whistle is to carry out a corresponding signal compensation. With this feedback compensation approach, the feedback path is digitally simulated and its effect is compensated. These approaches for feedback reduction may, however, markedly corrupt the output signal audibly, in particular if the input stage of the acoustic system is only designed for a small spectral bandwidth.
Acoustic systems with a narrow-band input stage further have the drawback that the acoustic quality of the output signal is generally correspondingly low.
A method and a device for noise suppression in a redundant acoustic signal is known from the publication EP 1 304 902 A1. In this case, a sub-frequency range of the input signal, in which interference is concentrated, is removed. Subsequently, the intensity of the remaining input signal is split into an input signal element to be retained and an input signal element to be processed further. Due to the input signal element to be processed further, the removed sub-frequency range of the input signal is synthesized. Finally, the input signal element to be retained and the synthesized input signal element are combined to produce an output signal with reduced interference relative to the input signal.